Introduction
The present invention relates to a vibration sensing device for use in many operations such as for security or safety equipment. The present invention is particularly related to vibration sensing devices of the type comprising an inertia mass on a support assembly which includes an electrical monitoring circuit closed by the inertia mass on the support assembly.
Vibration sensing devices, often called inertia sensing devices or accelerometers are used extensively for mamy operations. For example, they are used for security equipment and for safety equipment. These vibration sensing devices are switches operated by movement of the switch as a whole under the influence of an accelerating force, for example, any vibration, impact or other accelerating force.
Such vibration sensing devices may be used on machines to ensure that the machines are cut out once they exceed a predetermined amplitude of oscillation due to some over or eccentric loading. Similarly they may be used on vehicles in the event of a crash or of unauthorised interference.
In security equipment they are used for detecting vibrations in a window or door caused by an intruder in the building or by an attempted break-in.
Briefly, such vibration sensing devices when used in a security system consist primarily of two elements, a detecting loop namely, the sensor or vibration sensing device and an analysing circuit. Such devices, for example, are well known as shown in British Pat. No. 1,263,076 which describes a particular vibration sensing device and British Pat. No. 1,441,563 which describes a particular analysing circuit. Similarly, my previous U.S. Pat. No. 4,185,180 describes a vibration sensing device which includes a pair of spaced-apart electrically conductive plates each having an annular track formed by a hole. An electrically conducted bar is mounted between the plates on the tracks. On sensing vibration the bar will resonate, lifting off the tracks, thus making and breaking the electrical circuit between the plates.